This invention relates to high power testing of microwave transistors (DUT) in nonlinear operation, especially, but not only, where harmonic signal components are generated and must be processed. When the transistor is driven in its nonlinear operation regime, the internal impedance at the output of power transistors is very low. An impedance tuner used to match the transistor must also physically conjugate match such impedance. Passive impedance tuners can reach maximum reflection factors |Γtuner| of the order of 0.95, corresponding to smallest impedances of 2.4 Ohm. The insertion loss of the RF connection between DUT and tuner reduces this available tuning range at the DUT reference plane and thus the capacity of the passive tuner to match the transistor. The only remedy to this limitation is using active systems, i.e. test systems whereby a signal coherent with the signal departing from the DUT, is returned and re-injected independently into the DUT output and creates a virtual (not a physical) load. This additional signal can be the only one injected, in which case we speak of “active” or “purely active” load pull, or it can be superimposed to signal physically reflected by a passive tuner, in which case we speak of “hybrid” load pull; obviously if only a mechanical or electronic (PIN diode based, see ref. 5) tuner is present, we speak of “passive” load pull. In both pure active and hybrid load pull cases the objective is reaching and conjugate complex matching the internal impedance of the DUT (transistor); in general terms a standard requirement is a dynamic range reaching a reflection factor |Γ|=1 (corresponding to the real part R of 0 Ohm (Ω) of the associated impedance Z=R+jX). The objective of this invention is a compact hybrid tuner apparatus, combining an internal forward signal sampling and active feedback injection mechanism within a single tuner housing architecture, allowing |Γ|=1. Harmonic signal components are also processed (matched with proper loads) using only the passive harmonic tuner capability.
The typical prior art test active injection system is shown in FIG. 1: In this prior art hybrid (=active/passive) test setup the signal source of the four-port vector receiver 24 (VNA), injects signal 25 into the DUT 21 via a source impedance tuner 23 and a bidirectional coupler 11. Similar to ref. 6, the outgoing signal travels through a second bidirectional coupler 10 and a load impedance tuner 20 to a directional coupler 26, which allows injecting signal power 27 from a second, independently controllable, but synchronized with the first, source of the VNA towards the DUT. The signal path terminates with characteristic impedance Zo 19, typically 50Ω. The commonly designated injected (<a>) and reflected (<b>) power waves from and into the DUT ports (<a1> into- and <b1> from-the input port and <a2> into- and <b2> from-the output port) are measured by the VNA 24, after being sampled by the couplers 10 and 11. The tuners and instruments are controlled using data communication cables 18 and 17 by a system controller 22 running appropriate test software.